I dislike strawmans so this argument always irks me.

Teachers are left leaning because people with left leaning predilections tend to choose teaching as a career. There are multiple models to explain this but the most relevant is the idea that lefties tend to order their moral hierarchy “outward in” (World > Society > community > family > self) and righies tend to reverse that order (self > family > community > society > world)

The type of person that morally prioritizes the broader world & society will be more inclined to learn about it and also to teach it.